Ovulation rate and egg recovery in cattle treated repeatedly with pregnant mare serum gonadotrophin and prostaglandin.

Fourteen heifers were superovulated five to 10 times using pregnant mare serum gonadotrophin (PMSG) and prostaglandin in a standardised regime which resulted in a mean interval of 42.1 days (SEM +/- 0.97) between treatments. There was a significant (P less than 0.02) fall in the mean ovulation rate at the second treatment when compared with the first but no significant difference between mean ovulation rate at the second and subsequent treatments. No significant difference between treatments in mean egg recovery rate or in the percentage of normal eggs recovered was demonstrated. Four heifers treated 10 times continued to respond with multiple ovulations on most occasions. At the end of the experiment 13 of the 14 heifers were inseminated and 12 conceived, requiring a mean of 1.67 services per pregnancy.